IN THE DEGRADATION OF THE LITHOSPHERE. 367 



(d) Boundaries of geological formations.^^ 



(e) Tectonic control of earthquake shocks. ^^ 



(/) Atmospheric weathering such as in the Grand Canyon, bowlder 



weathering, etc. 

 (g) Shore Hnes.^^ 



(//) Valley formation due to faulting under joint control.^* 

 (/) Grand features of the earth as related to lines of fracture and 



block movements resulting therefrom. ^^ 

 ( y ) Plateau fracturing and disintegration.^" 



Other literature might also be cited but these references are deemed 

 enough for the immediate purpose of illustration. 



It is evident, then, that systems of fracture along definite lines 

 of direction extending both over wide areas of country and in 

 lines of great length, are to be regarded as playing a major part in 

 lithosphere evolution, and that jointing must be regarded as one of 

 the active agents at work in the behavior of the lithosphere. 



The discussions in the literature of the science concerning the 

 origin and nature of fjords illustrate probably as well as any one 

 phase of the subject the attitude of writers toward the relation of 

 joints to earth-structure. Giinther^^ gives a resume of the discus- 

 sions of theories regarding fjords and groups them into the follow- 

 ing classes : The Depression Theory, the Cleavage or Fracture 

 Theory, the Glacial Theory, the Erosion Theory. It will be noted 

 that all but one of these theories seek to explain the origin of fjords 

 upon some basis really exterior to the nature of the lithosphere con- 



1- Hobbs, "Earthquakes," New York, 1907, passim; includes also refer- 

 ence to other joint literature. 



13 Shaler and Tarr, " Geology of Cape Ann, Mass.," 9th Ann. Rep. U. S. 

 G. S.. 1887-88, pp. 529-611. 



1* Kemp, "Preliminary Report on the Geology of Essex County, N. Y.," 

 Report N. Y. State Geol. Survey, 1893, pp. 438 ff. 



15 Hobbs, Bull. Geol. Soc. Amer., Vol. XV., pp. 503-506. 



16 E. Erdmann and Nathorst, Erdmann, " Descr. de la form. carb. de la 

 Scania," 1873, Royal Swed. Geol. Institution. Nathorst, " Geol. Foren Stock," 

 IX., pp. 74 ff. See also Suess, " The Face of the Earth," Vol. 2, especially 

 for resume of these papers and also discussions of the structures of the Cana- 

 dian and Baltic shields. (The English translation by Sollas is the one re- 

 ferred to.) 



1" Giinther, " Lehrbuch." Vol. II., 1882, pp. 463 ff. 



